In an OFDM modulated signal which has conventionally been known, a unit of the signal transmitted at once is referred to as a frame. At a start of the frame, preambles are arranged followed by data symbols. The preamble includes short training sequences (STSs) and long training sequences (LTSs). It should be noted that, in an OFDM modulated signal employed by the IEEE 802.11a standard for a wireless local area network (LAN), a symbol “SIGNAL” is inserted between the preambles and the data symbols. The symbol SIGNAL is a symbol which indicates the number of data symbols in one frame, and a modulation scheme for the respective data symbols.
A modulation accuracy has conventionally been analyzed by demodulating the OFDM modulated signal (refer to Japanese Laid-Open Patent Publication No. 2003-324406, for example). According to IEEE 802.11a, upon the analysis of the modulation accuracy, it is specified that 20 or more frames which include 16 or more data symbols are to be measured. It should be noted that the frame is transmitted as a burst signal.
However, for the analysis of the OFDM modulated signal according to IEEE 802.11a, it is necessary to carry out a frame detection process at least twenty times. Moreover, it is also necessary to process the preambles and the symbol SIGNAL. Thus, it takes a long time to analyze the modulation accuracy of the OFDM modulated signal.
It is therefore an object of the present invention to reduce the time required for analyzing the modulation accuracy of a modulated signal.